[bassislife]

> A good type system (e.g Rust's, Haskell's..) can eliminate all type errors from your programs.

It will eliminate errors related to the use of a given programming language. It will not necessarily avoid systemic errors. The programming language is only one part of the problem. Safety is a wider issue than just the use of a programming language.

Especially since the systems we use are often dynamic with changing requirements.

[rkrzr]

> It will eliminate errors related to the use of a given programming language. It will not necessarily avoid systemic errors.

Like I said: It will eliminate a specific class of errors, namely all type errors. Your program will literally not compile if there are any type errors.

> The programming language is only one part of the problem. Safety is a wider issue than just the use of a programming language.

Sure, I don't disagree with that statement. But it's important to recognize that eliminating whole classes of errors is extremely valuable and allows us to focus on the important things.

[ytugiuyghvk]

Every type system eliminates all its own type errors by definition. Even the trivial system with one type eliminates all its own type errors (vacuously, since there are zero of them).

There is no universal set of errors called type errors. What are type errors depend on your type system. A good type system allows more errors to be encoded as type errors so you can catch them at compile time, but it doesn't mean anything to say that a language like Rust or Haskell eliminates all type errors. There are certainly type systems which could catch more errors.

[rkrzr]

Sure, not all type systems are created equal. And there are indeed type systems that can catch more errors than Haskell's (although that usually comes at the price of losing type inference).

But I read OP's point as "Well, you can never catch all programming errors with PL_feature_X, so why even bother." And my point is simply that a lot of PL features make formerly hard things easy and thus allow you to go faster and focus on more interesting things.

[braveo]

You completely misunderstood what he was trying to tell you.

[msbarnett]

There was nothing interesting in what he was trying to say.

Yes, no programming language perfectly eliminates all classes of unsafety. But that's no reason to let the perfect be the enemy of the good! "The issue with safety is..." no issue at all. Being safe in a bunch of problem domains (Rust) is still strictly better than being safe in very few if any of them (C).

[braveo]

So you did it on purpose. That just makes you a bad actor in the conversation.

[ssalazar]

More to the point, Rust and other statically typed languages* eliminate type errors at compile-time.

In e.g. Python, the following code:

    foo = Bar()
    foo.baz()

will compile without complaint but, supposing that baz() is not a member of class Bar, will cause errors when the code is actually run. In statically typed languages this will be caught by the compiler and treated as an error; type errors are simply not allowed in compiled programs.

This distinction is significant, as Python and other dynamically-typed languages require comprehensive test suites for any non-trivial software written in them, shifting the burden of ensuring type safety to the programmer. Testing systems for statically typed languages don't need to concern themselves with type safety. Dynamic typing also carries performance penalties at run-time (checking type safety for e.g. every member access).

* Some statically-typed languages (e.g. C++) allow for very specific subversions of type safety at run-time, but its usually clear to the programmer when they are doing something dangerous.

[jibalt]

"but its usually clear to the programmer when they are doing something dangerous"

Um, no. Every pointer is fundamentally unsafe, and a lot of C++ code is written with pointers through and through.

[jibalt]

"Every type system eliminates all its own type errors by definition."

Nonsense. C/C++ will happily produce a warning, if you specified -Wall, that you violated a type constraint and then go ahead and compile your program. To suggest that such violations are part of C's type system is to pedantically and willfully miss the point.